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Advice On Fitting An R C B O


tictag
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As part of my new solar project, I need to fit a new circuit breaker to separately supply the Alde so that it is not powered when/if the inverter kicks in. Because space in the PDU is limited, I was considering using a combined RCBO device rather than having a separate RCD and MCB, rated at 16A overload & 30mA leakage. I am trying to get hold of one manufactured by the same company as those already present i. e. NBSe – this, however, is proving to be challenging.

 

So to the query. I’d like to do the work myself but I’m concerned that there maybe things I don’t know so I’m reaching out to you lot for advice. Some queries to start us off:

  1. Would a 16A / 30mA RCBO be suitable for this purpose?
  2. If I struggle to source an NBSe brand, could I fit any brand of a similar spec?
  3. Is there a specific spec for mains cable in a caravan i. e. resistant to vibration? I know from a previuos project that twin’n’earth is a no-no! ;)
  4. Apart from just good electrical practice (bend radius, no damaged strands, heatshrink boots, PAT testing, protection from chaffing etc) are there any particular regulations that I might not be aware of?

I’m planning to get an certified electrician to check my work once completed.

 

Any advice would be gratefully received.

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Hi

 

Not being pedantic, but seem to remember in one of your threads that you said your brother was a qualified electrician, surely his advice and knowledge would be better than asking on an open forum ?, Sorry if I got it wrong

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I'll take advice from anywhere I can get it :) And this forum is filled with electricians that specialise in caravans. I think I'd be a fool not to ask.

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I'll take advice from anywhere I can get it :) And this forum is filled with electricians that specialise in caravans. I think I'd be a fool not to ask.

Quite right too.

 

Could you not simply fit a relay that's energised when the inverter is running which then removes the supply from the alde and battery charger etc ?

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Sure to be barking up the wrong tree ere but:

 

Doesn't the Victron inverter/charger have 2 outputs? One that is used as a UPS and supplies 240v which has been inverted from the battery supply, and one AC out that dies with the shore supply - I thought this was where you were supposed to connect heaters/alde or anything that didn't require the uninterrupted 240v supply. I presumed the 240v shore supply would be routed through your main RCD and into the Victron.

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Could you not simply fit a relay that's energised when the inverter is running which then removes the supply from the alde and battery charger etc ?

 

That's essentially what the inverter has. Two outputs, only one of which s supplied with 'inverted' mains when the main supply i. e. EHU is lost (or was never there).

 

 

Doesn't the Victron inverter/charger have 2 outputs? One that is used as a UPS and supplies 240v which has been inverted from the battery supply, and one AC out that dies with the shore supply - I thought this was where you were supposed to connect heaters/alde or anything that didn't require the uninterrupted 240v supply. I presumed the 240v shore supply would be routed through your main RCD and into the Victron.

 

That's bang on, SF. My assumption is that the inverter effectively outputs into 2 x 3-core cables, both are supplied by EHU when it's available, only one is supplied by the inverter output when it's not. I need to connect the non-inverter output to the Alde and I figured the best way of doing this would be to connect that output directly to an MCB, which in turn supplies the Alde. But I also want the protection an RCD affords so figured a combined RCD/MCB (i. e. an RCBO) would be best. If I used the main PDU RCD, at some point I would need to separate the supplies and I'm back with the 240v relay thing.

 

I'm not sure if that makes any sense!!

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Energise the relay coil with the non inverted output of the inverter, put the relay in series with the supply to the alde. If you have hook up, the relay will be energised and fed from the normal breakers including rcd. When why isn't there, the relay is open and therefore mains is not available to the alde.

 

Ap

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Yes, this would work if the inverter supply output was only live when the inverter was activated, in fact it's always live. When EHU is present it feeds this through and switches to inverter output only when it fails - it's designed to be a UPS, switches supply in 10ms or something similar.

 

The loss of power to the normal AC out could be used as the signal, though the relay would have to be permanently energised; loss of power would de-energise it, switching out the Alde.

 

I think both solutions are perfectly valid i. e. separate supplies & relay. It might just boil down to cost i. e. relay versus RCBO and practical matters e. g. where to site a mains relay.

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The RCD within a RCBO can have the same properties as separate units the main difference is RCBO’s are often single pole switching even though both cables go through the unit. There are some places where you need all pole switching. 721. 411. 1 says this type is required with a caravan. There is also three main type.

▪ AC type, for alternating current only
▪ A type, for alternating and/or pulsating current with DC components
▪ B type, for alternating and/or pulsating current with DC components and continuous fault current.

With inverters should be A type rather than AC.

Consumer units are type tested distribution boards if you don’t fit items recommended by the manufacturer then it is no longer type tested, so no longer a consumer unit, so should not be used where ordinary people are in control. Personally I would not be worried about that many people do fit other makes of MCB, RBCO, and RCD but strictly speaking you should not. All RCD’s are not equal they should hold in at 50% of the rating so should trip between 15ma to 30ma but some like the X-Pole will hold at 90% to 100% so less likely to trip and they also give indication before they trip.

 

As to wiring it states:-

“721. 521 Types of wiring system
721. 521. 2 The wiring systems shall be installed using one or more of the following:
(i) Insulated single-core cables. with flexible class 5 conductors, in non-metallic conduit
(ii) Insulated single-core cables, with stranded class 2 conductors (minimum of 7 strands), in non-metallic conduit
(iii) Sheathed flexible cables.
All cables shall, as a minimum, meet the requirements of BS EN 60332-1-2.
Non-metallic conduits shall comply with BS EN 61386-21.
Cable management systems shall comply with BS EN 61386.”

Also it states min 1. 5mm. (721. 524. 1) Personally I would use any flex and would not worry about the BS-EN numbers.

“721. 522. 7. 1 As the wiring will be subjected to vibration, all wiring shall be protected against mechanical damage either by location or by enhanced mechanical protection. Wiring passing through metalwork shall be protected by means of suitable bushes or grommets. Securely fixed in position. Precautions shall be taken to avoid mechanical
damage due to sharp edges or abrasive parts.” Common sense really.

As to testing you need special meters able to measure time as well as current it has to trip within 40ms at 5 times rated current. All tests done are both pos and neg half cycle however if it trips with button then likely good enough until you can borrow a tester.

Unless grid-tie inverter is used then a positive method to ensure both systems can’t be used together. The older star/delta contactors did have a mechanical interlock and there are special change over switches, but normally simple two sockets and one plug method is used. I do not like automatic change over relays there needs to be an inbuilt delay to stop chattering.

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The Victorn kit has arrived and it looks like I've made a mistake on the inverter specs :( Lesson learned. The second AC outlet is only fitted to the 3 & 5 KVA models, not the 1. 8KVA model I've purchased. This means that there is only one AC outlet that has either EHU/Genset output fed through or automatically switches to Inverter output should it fail (UPS). So how do I switch out the Alde?

 

All I can come up with is AudiPartner's relay solution in series with the Alde but fed directly from the EHU input. If EHU is available, Alde is switched in, if it fails, Alde mains element is switched out. Can you get mains supplied relays i. e. they rectify the AC themselves?

 

How fast does a mains relay de-energise? The Inverter switches supplies in 20ms according to the specs. Would there be a short time where the inverter is actually powering the Alde before this relay de-energises? If I've got the Alde on the 3KVA, setting, whilst it's still within the peak power specs of the inverter, that's one hell of power spike!


p. s. Really good quality kit, by the way. Everything feels like it would outlast me.

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I was thinking of something like this:

 

system schematic v2.0

 

I've identified a suitable 230V 16A double-pole-double-throw 35mm DIN mountable relay here: http://uk. rs-online. com/web/p/non-latching-relays/2928427/ Uses 10mA at 230V to keep the coil energised.

 

Edit: Added relay details.

Edited by tictag
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What fault protection are you planning for the relay feed? Seems like a reasonable solution to me, I guess the next size of inverter is quite a bit more so changing for the model with two outputs is not an option?

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Interesting that you should ask that because I realised another niggle in my design earlier. The output of the version of MultiPlus I've bought is limited to 16A at 230V so to answer you question, the relay contacts are protected by a 16A MCB in the PDU, the RCD in the PDU and a 16A / thermal breaker in the inverter. I hadn't considered protection for the relay coil, maybe a simple 20mA in-line fuse?

 

The niggle is this 16A output limit; this applies to AC being fed through from the EHU/genset. The Alde on full whack (3KW) is eating up 12A so all I then need to do is run a kettle and I'll be approaching this limit. Now maybe it's not a problem because I've never been on a site that's had more than a 16A EHU and my genset isn't even capable of producing 16A but the power sharing feature of the inverter supplements primary supply (e. g. EHU) with inverted supply if it is not capable of meeting demand so in this scenario the 16A limit may well be breached.

 

The model up allows 30A and has the two AC outputs but it's physically very much bigger (and heavier) and, practically speaking, I just don't need a 2KW output.

 

If I want this system, I think I'm just going to have to accept a 16A limit.

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I thought I read that you could manually program through the controller panel the current limit being supplied from the batteries and drawn in total, I figured this was to prevent nuisance tripping which is what your niggling about, might be I've read the wrong spec but I'm sure you had the plug in control panel as well didn't you?

 

I think I would forget about using the Alde on max, I saw on their website max current draw of 14A on 3kw setting (it says 3. 2kw in brackets for some reason), 2kw must be ok, our 2kw fan heater heats the van in about 30mins when we get back in.

 

I know everyone raves about alde (and yes I do have blown air!) but it seems to be very thirsty, 0. 5kg of gas an hour or 14A on full blast!

Edited by sleepyfolk
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Yes, the control panel is a must, if only to configure the settings. And you're right, you can set the primary supply threshold e. g. 10A. If the threshold is reached, the inverter will initially reduce the charging current to honour the AC demand (power control) and if this isn't enough it will supplement the primary power with 'inverted' power from the battery (power assist).

 

But the point I was making is that overall the AC output of this model is circuit breaker limited to 16A whereas, for example, the RCD in the PDU is rated for 25A, which means that this inverter is imposing a stricter limit on AC power than currently exists.

 

And you're right, of course, do I really need 3KW output from the Alde? It might take slightly longer to warm the 'van but that's not exactly a hardship!

 

 

p. s. I have no other experience than the Alde so can't really comment on it's performance over blown air.

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Is that to tie in with the limit on an EHU being 16a though, seems odd that, I thought you would be able to supersede the 16a post limit occasionally because the unit supplemented the power with the battery when the supply drawn from the ehu reached the set limit, this would have let you have 3kw and a kettle for a short period whilst discharging the battery briefly.

 

Seems a quandary, is the 16a limit an issue if the ehu has that limit and the genny is unable to exceed16a?

 

Where's everyone gone? We need a supergeek.

Edited by sleepyfolk
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And you're right, of course, do I really need 3KW output from the Alde? It might take slightly longer to warm the 'van but that's not exactly a hardship!

 

I regularly use a 10 amp HU and on cold days gas & mains to start up. Gas goes off of its own accord very quickly once raised fluid to temp when, of course, 2Kw is ample. Surprised me how quickly the combined fuels work.

Edited by SamD

Sam :beardy:

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Seems a quandary, is the 16a limit an issue if the ehu has that limit and the genny is unable to exceed16a?

 

No, it's actually much more simple than that :) The inverter's AC output simply goes out via a 16A circuit breaker! So, yeah, almost doesn't matter what the EHU post is rated at, the inverter will try to cover whatever mains demand is placed on it. .....but, and here's the nub of it, only up to 16A. Which means that my caravan's usage, irrespective of mains source (EHU, genset, inverter), cannot with this model inverter at least exceed 16A.

 

But the thing is, whilst I'm not so keen having restrictions placed on my new system, is this really a problem? 16A concurrent use is a lot for a caravan; even the Alde isn't on all the time.

 

I suppose I'm just a little frustrated that I didn't recognise this in my design.

Edited by tictag
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I regularly use a 10 amp HU and on cold days gas & mains to start up. Gas goes off of its own accord very quickly once raised fluid to temp when, of course, 2Kw is ample. Surprised me how quickly the combined fuels work.

 

Yes, another good point. If 2KW isn't working fast enough, I can supplement with gas. In fact, now that I recall, I was on on a 6A EHU in Ireland last autumn and couldn't even use the 2KW setting - the 'van was still warm. I think 16A will be fine.

 

I've started the build, btw, crimped my first 50mm2 heavy duty crimp last night! (sorry, wrong thread to talk about that!)

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I suppose I'm just a little frustrated that I didn't recognise this in my design.

I know what you mean, it's annoying when it's just not quite what you planned, if you don't exchange the victron for the bigger one its still going to do what you wanted it to in the main, we still look forward to the install!

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I wonder what consumer unit you are using? Some caravan specials have battery charger built in and are rather inflexable but with a standard 17th edition consumer unit normally two RCD's if instead of supplying both from the isolator one is connected to inverter and the other to a second 16A plug and you make a splitter lead so with just a EHU supply you use splitter lead to feed both plugs but you can also feed seprate if required so solar panel and battery feeds everything but heater and generator or site power feeds heater.

 

You will never feed heater from inverter so why wire it so it can be fed? Keep it simple two plugs and a Y lead so can feed both plugs from same supply.

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I wondered about splitting the supply out from the back of the incoming 240 ehu socket and taking the supply to a mini consumer unit with the rcbo in that just powered the heating so it would only be live if the external supply was connected

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Interesting read, (and i am no expert) but i do think things are getting a bit complex for the requirements. A 3kw inverter (assuming a 3kw Alde) is going to flatten and maybe damage the battery, would i be right in thinking that the inverter would draw around 180a? You could as has been pointed out reduce the current draw via the Alde control panel and use a smaller inverter but even on 4a the power draw would still discharge the battery quickly and this is before other 12v equipment is considered.

My thoughts would be a split 230v input to a seperate CU. 16a CB to current fused spur. (all to current 17th standard). The Alde could be left switch on 240v perm and gas also selected so if power lost then heater would automatically select gas as primary power source.

From a practical angle, the time, effort, reliability and cost would be in excess of simply using the heater on LPG.

Apologies if i am missing something in OP`s requiremnts

 

I have done some work with UPS in industry. Both used a large bank (100+)of batteries to run the plant until genny flashed up (a 1. 2MW diesel) and the other was a complicated gas turbine genny which required all sorts of valves,relays,prayers and mostly good luck to get going. A power interuption, even a decent flicker made for some frantic activity from us reactive engineers.

Gem Caravans (Fife) Ltd.

ALL MAKES SERVICING AND REPAIRS

BAILEY TRANSIENT WARRANTY, LUNAR AND COACHMAN WARRANTY

www. gemcaravancare.co.uk 07803 922945

WORKSHOP NOW OPEN

 

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I agree with dougie but must point out any RCBO does need to be all pole switching the types used in a house are no good as they do not switch the neutral I have struggled to find a consumer unit that will take all pole devices and in the past I have used a three phase distrubution unit leaving one phase empty but room is limited in a caravan so not really the answer. Although one could use 16A RBCO's to replace the RCD in a standard domestic unit can't see this really helps as you still have a row of MCB's. In theroy a three unit wide CU with a 16A RBCO and a 6A MCB would give all that is required in most caravans but in the main even the smallest CU is four units wide so may as well have RCD feeding a 16A and 6A MCB. In most caravan sites the supply is already from a RCD protected unit so multi RBCO's are no advantage so in real terms can't see how a RCBO in a caravan helps?

 

Also as already stated you need A type with inverters not AC type and getting an A type RCBO would be rather hard.

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You will never feed heater from inverter so why wire it so it can be fed? Keep it simple two plugs and a Y lead so can feed both plugs from same supply.

 

 

I wondered about splitting the supply out from the back of the incoming 240 ehu socket and taking the supply to a mini consumer unit with the rcbo in that just powered the heating so it would only be live if the external supply was connected

 

You are of course completely right and your comment, "You will never feed heater from inverter so why wire it so it can be fed?" is quite valid; a separate supply via an RCBO would be a far better solution than the relay, there is a "but", however. ...

 

One of the features of my system design is that should the site EHU not be able to provide the power being demanded, my inverter will sense this and supplement the EHU with power from the inverter. This is called PowerAssist in Victron terminology. If I supply the Alde separately then the inverter won't know there is too much demand and I'll end up tripping the post. So whilst it makes perfect sense, powering the Alde separately will not allow my system to function per its design.

 

This PowerControl / PowerAssist threshold is configurable via the control panel. By default it's set to 12A but can be configured from 2. 7A to 16A.

 

 

Interesting read, (and i am no expert) but i do think things are getting a bit complex for the requirements. A 3kw inverter (assuming a 3kw Alde) is going to flatten and maybe damage the battery, would i be right in thinking that the inverter would draw around 180a? You could as has been pointed out reduce the current draw via the Alde control panel and use a smaller inverter but even on 4a the power draw would still discharge the battery quickly and this is before other 12v equipment is considered.

 

Slight misinterpretation of the system design. I never want my inverter to power the Alde, I've got gas for that and, as you quite rightly suggest, it'll flatten the battery(ies) very quickly. But I do want to power the Alde from EHU (as is normal). Thing is, my inverter is also a UPS so if the EHU fails for any reason, the inverter will kick-in automatically and, if the Alde was on, it would then draw power from the inverter, which I don't want. Separately powering the Alde is a potential solution but as pointed out above, this reduces some of the functionality my system design offers.

 

 

Any more advice / guidance would be very welcome but as it stands I'm left with AudiPartner's relay solution energised by a EHU/genset supply being available.

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